Removal of non-diamond carbon from a surface of a substrate has been accomplished in the past by wet chemical etching and by reactive ion etching.
Wet chemical etches cannot be masked with a photoresist since such etches also attack the known photoresists even more quickly than the non-diamond carbon. In order to use a wet chemical etch to pattern a non-diamond carbon layer, all non-diamond carbon must be either removed or portions thereof masked with an inert substance like silicon dioxide, which is difficult to do because wet chemical etches, such as boiling chromic acid-sulfuric acid mixtures, are non-selective chemicals and are difficult to work with.
Reactive ion etching or ion beam assisted etching produce energetic ions which can be used to selectively remove portions of non-diamond carbon down to the substrate surface. This is done by placing a mask or a metal pattern on a layer of non-diamond carbon disposed on a substrate and directing the energetic ions at the non-diamond carbon on the substrate. Removal of the exposed non-diamond carbon is facilitated by the energetic ions. The use of energetic ions to selectively remove non-diamond carbon results in damage to the underlying substrate surface making it less useful for electronic applications.
Partial removal of non-diamond carbon is usually used to form patterns of non-diamond carbon on a substrate. This result can be achieved with ion beam implantation. Pursuant to this procedure, a metal shadow mask is placed over a substrate devoid of non-diamond carbon thereon and then carbon, nitrogen, argon, helium or other ions, but preferably carbon ions, are directed at the mask. The mask metal protects the underlying surface from the ion beam but in the exposed portions of the mask, the high energy ions from the ion beam form electrically conductive non-diamond carbon, if the substrate is diamond. The problem with the use of shadow masking in ion beam implantation for patterning a subtrate is two fold: cartain patterns cannot be performed by this technique and resolution of the pattern done by this technique is poor. The patterns which cannot be done by this technique include the doughnut shapes and resolution of patterns obtained by this technique is generally 20-30 microns, which is poor by today's standards. Resolution generally denotes the smallest feature that can be made.